In an accompanying Information Disclosure Statement, we disclose a large number of fitness/muscle-strengthening weight systems. These include disclosures of various forms of hollow weight members which are fillable with water, sand or other fluids or fluent materials, some of which are collapsible and some of which are semi-collapsible. FIG. 1 discloses a commercially available water inflatable weight system marketed under the trademark AQUABELLS in which vinyl water chambers W have a valve V which is placed under a water faucet to fill the chamber with water. To remove any air pockets, the valve V is pulled up until the water overflows. Then the valve is closed so as to seal the water in and pushed back down so it will be flush with the sidewall. The weights W are then placed on a plastic bar B, and threaded plastic bolts PB are engaged with threaded ends TE of the plastic bar B to secure the weights in place. Foam material F cushion the grips.